title: Bis(1,3-dimethyl-1H-imidazolium) hexa-fluoro-silicate: the second monoclinic polymorph.
abstract: The title compound, 2C5H9N2 (+)·SiF6 (2-), (I), crystallized as a new polymorph, different from the previously reported one (Ia) [Light et al. (2007 ▶) private communication (refcode: NIQFAV). CCDC, Cambridge, England]. The symmetry [space groups P21/n for (I) and C2/c for(Ia)] and crystal packing patterns are markedly different for this pair of polymorphs. In (I), all imidazolium cations in the lattice are nearly parallel to each other, whereas a herringbone arrangement can be found in (Ia). In (I), each SiF6 (2-) dianion forms four short C-H⋯F contacts with adjacent C5H9N2 (+) cations, resulting in the formation of layers parallel to the ac plane. In (Ia), the C-H⋯F contacts are generally longer and result in the formation of layers along the bc plane.
authors.affiliation: College of Chemistry, Leshan Normal University, Binhe Rd 778, Leshan 614000, Sichuan Province, People's Republic of China.
authors.forename: Chong
authors.initials: C
authors.lastname: Tian
authors.forename: Wanli
authors.initials: W
authors.lastname: Nie
authors.forename: Maxim V
authors.initials: MV
authors.lastname: Borzov